Speaking to Rozen yesterday, Zelikow expanded on what happened:
I tried to raise consciousness that there was a massive potential problem here. 'Maybe we should do something.' And the answer to that was silence. 'We don't want to discuss this. We don't want to reassure you. We prefer to ignore you raised this.' I worked hard on this memo. I wish people had answered to tell me why we [dissenters] were so wrong.' But their preference was, 'Your intervention is so frivolous and out of school that it doesn't deserve a response.' That's too bad.
He also called for an independent commission to probe the torture program:
[O]ne of the reasons I support some kind of inquiry is to comprehend why so many people believed that a program like this was a good idea - since we now believe it was a mistake. So we can learn from the mistake. When there is this kind of collective failure, we need to learn from what happened.
He said it should be along the lines of the 9/11 commission that he himself directed:
That way you don't have a situation where [former ranking Senate Intelligence committee member] Jay Rockefeller and Nancy Pelosi are seen as being hypocrites. Turn over the inquiry to others. That is the way they can neatly address this argument, because they won't be the ones conducting the inquiry.
It's worth noting that Jonathan Turley, a professor at George Washington Law School and prominent advocate for a full investigation, has explicitly criticized the 9/11 commission as a model, saying its members were unwilling to assign blame, and were too concerned to with protecting the political reputations of those who selected them.
The testimony to be given by the other marquee witness, former FBI agent Ali Soufan, is here.